(1) Field of the Invention
This invention relates to equipment and a method for manufacturing a Hg--Cd--Mn--Te based single crystal.
(2) Related Art Statement
Recently, attention has been paid to an erbium doped fiber amplifier. The wavelength of 0.98 .mu.m is particularly expected to be an exciting wavelength for erbium. The bulky Hg--Cd--Mn--Te based single crystal is much expected as a material for an optical isolator with a wavelength of 0.98 .mu.m band. The range of a composition usable for an optical isolator is described in JP-A 7-233000, for example.
In the past, it has been difficult to grow a bulky Hg Cd--Mn--Te based single crystal using the Bridgeman process without breaking the crucible because of the high vapor pressure of Hg, which invariably raises the internal pressure within a crucible to such an exent as to cause breakage of the crucible.
JP-A 7-206598 describes equipment using a high pressure Bridgeman furnace, by which a Hg--Cd--Mn--Te single crystal is formed. The equipment has a heater above a crucible over the high pressure Bridgeman furnace to prevent the precipitation of Hg with higher vapor pressure in the crucible. JP-A-8-40800 discloses, a method for setting a material of single crystal in a container so that in THM method (traveling heater method), the production of a twin crystal may be prevented and the diameter of the thus obtained single crystal may be made large.
Although the mass production of single crystals with large diameters is known, along with the ability to prevent generation of a twin crystal, a difficult problem remains unsolved: Manufacturing a single crystal with a large diameter at a relatively low cost. This is because the vapor pressure of Hg increases in geometrical progression as its diameter becomes large, so that a high pressure Bridgeman furnace is used, and a container for forming the single crystal is required to be pressurized at about 30 kg/cm.sup.3.
Compositional segregation is, however, recognized in the single crystal, as viewed in its diametrical direction, and sometimes crystals with different phases are generated since a melt has differing states between the outer peripheral part and the center part. Thus, since the characteristics of such a single crystal as an optical isolator largely vary, it is difficult to obtain one single crystal satisfying the characteristics required of an optical isolator. Moreover, the optical loss character of the isolator varies due to the deviation in the crystal orientation of the single crystal.